I am not sure what did you mean with M/S so I googled it. Found an article "How to Use M/S Processing in Mastering" where it says that it's a mid/side technique. Followed the instructions there and created 2 more tracks with the solo part: 1 panned hard left, the 2nd panned hard right, and the centered one already was there.
Can't use chorus as this effect changes the timbre of my instrument in an unnatural way.
Rendered again and the solo instrument track still can be canceled.
Then, I read the same article again it seems that I forgot to invert one of those 2 new created channels. After I did a phase reverse on the channel hard panned right, the instrument track wasn't cancelled anymore.
Now I just must raise the volume of that phase reversed track because it sounds lower than the left track.
Do you have more tips? Should I add a bit of delay on some of the mono tracks hard panned?